1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to a target object; and, in particular, to an active type rangefinder apparatus used in a camera or the like.
2. Related Background Art
Conventionally known as an active type rangefinder apparatus used in a camera or the like is one having light-detecting means for detecting light reflected from a target object and outputting near-side and far-side signals corresponding to the distance to the target object, comparing the far-side signal with a preset clamp signal in terms of magnitude, calculating an output ratio signal from the ratio between the greater signal determined by the comparison and the near-side signal, and converting the output ratio signal into a distance signal according to a converting expression varying depending on the value of output ratio signal as disclosed in Japanese Patent Application Laid-Open No. HEI 10-274524.
This rangefinder apparatus is aimed at obtaining rangefinding results on a par with those of a conventional system using both the light quantity and rangefinding in a short period of time without enhancing its circuit scale, so as to determine the distance to the target object uniquely and stably even when the distance is long.
Meanwhile, in a signal processing IC for signal processing and the like in this kind of rangefinder apparatus, power-on resetting is carried out at the time of starting a rangefinding routine in order to initialize data. Also, there are cases where a reset signal is fed into the signal processing IC from a microprocessor and the like.
If power supply to the signal processing IC is stopped and then power is fed again before the supply voltage becomes zero, however, then there is a case where power-on resetting is not effected in the signal processing IC. In this case, data will not be initialized in the signal processing IC, whereby there is a fear of normal rangefinding failing and malfunctions occurring.
If a reset signal is to be fed into the signal processing IC for resetting, then it is necessary to provide the signal processing IC with an input terminal for the reset signal. From the viewpoint of cutting down the cost of signal processing IC and so forth, however, it is desirable that the number of I/O terminals in the signal processing IC be smaller.
In order to overcome such technical problems, it is an object of the present invention to provide a rangefinder apparatus which can prevent malfunctions from occurring and can cut down the cost.
For achieving such an object, the rangefinder apparatus in accordance with one aspect of the present invention comprises light-projecting means for projecting a light beam toward a target object; light-receiving means for receiving reflected light of the light beam projected to the target object and outputting a signal corresponding to a distance to the target object; signal processing means for processing the output signal of the light-receiving means; and control means for outputting a control signal for the signal processing and a clamp setting signal for setting a clamp level to the signal processing means, and a reset signal for resetting the signal processing means to an initial state to an input terminal identical to that for the clamp setting signal.
According to this aspect of the present invention, the clamp setting signal and the reset signal are supplied to the same terminal of signal processing means, so that the number of input terminals installed in the signal processing means can be reduced, whereby the cost of signal processing means and, consequently, the cost of rangefinder apparatus can be cut down.
The rangefinder apparatus in accordance with another aspect of the present invention comprises light-projecting means for projecting a light beam toward a target object; light-receiving means for receiving reflected light of the light beam projected to the target object and outputting a signal corresponding to a distance to the target object; signal processing means for processing the output signal of the light-receiving means; and control means for outputting a reset signal for resetting the signal processing means to an initial state after power is supplied to the signal processing means but immediately before the power supply is stopped.
According to this aspect of the present invention, the signal processing means is reset immediately before the power supply to the signal processing means is stopped, so that a normal rangefinding routine can be carried out even when power is fed again before the supply voltage becomes a predetermined voltage or lower without power-on resetting, whereby the rangefinder apparatus can be prevented from malfunctioning.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.